Multipoint teleconference system employing H. 221 frames

ABSTRACT

A multipoint teleconference system dispensing with an MCU, in which terminals are connected into a loop configuration through an ISDN in such a way that each terminal is coupled with each of the adjacent terminals by a single B channel. Thus, a communication frame is revolved through a looped communication channel. Each terminal enters control information for controlling a multipoint teleconference, into a predetermined area within the communication frame, and it relays the resulting communication frame to the next terminal.

This is a continuation of application Ser. No. 08/372,133, filed Jan.13, 1995, now U.S. Pat. No. 5,604,738, which is a continuation ofapplication Ser. No. 07/913,403 filed Jul. 15, 1992, now U.S. Pat. No.5,402,418.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a teleconference/telephone terminal.More particularly, it relates to a multipoint teleconference systemwherein a conversation or a conference is held by connectingteleconference/telephone terminals at three or more multiple points orspots.

2. Description of the Related Art

As a multipoint teleconference system in the prior art, there has beenknown one proposed in the CCITT (International Telegraph and TelephoneConsultative Committee) Recommendation H. 320.

In order to realize a multipoint teleconference, the multipointteleconference system is equipped with an MCU in addition toteleconference/telephone terminals (hereinbelow, simply termed "ends").Herein, the multipoint teleconference is held in such a way that all theends to attend this teleconference are connected with the MCU, and thatthe MCU controls communications among multiple points.

Since the prior-art multipoint teleconference system realizes themultipoint teleconference as stated above, it poses the followingproblems:

(1) The number of ends which can attend the multipoint teleconference,and the transmission speed of the communications are limited by theadmitting capacity of the MCU.

(2) Even in the state in which all the ends of the pertinent group canattend the multipoint teleconference, this teleconference cannot be heldwhen the MCU is not operating or when all available MCU's are busy oroccupied for the multipoint teleconferences of other groups.

(3) In a case where the MCU lies at a point distant from the ends whichattend the multipoint teleconference, the communications becomeexpensive.

SUMMARY OF THE INVENTION

The present invention therefore has for its object to provide amultipoint teleconference system in which a multipoint teleconferencecan be realized by only the ends attending this teleconference, withoutrequiring any MCU.

The present invention consists of a multipoint teleconference systemhaving an ISDN in which frames stipulated in CCITT Recommendation H. 221(hereinbelow, termed "H. 221 frames") are transferred along setchannels, and a plurality of video telephone/teleconference terminalswhich conform to CCITT Recommendation H. 320 and which are connected tothe ISDN. The characteristic features of the present invention are asfollows.

At least one of the plurality of video telephone/teleconferenceterminals comprises a channel setting device for setting the channelsamong the individual video telephone/teleconference terminals within theISDN so that the plurality of video telephone/teleconference terminalsmay be connected in a ring configuration, and each videotelephone/teleconference terminal comprises a relay device for relayingthe received H. 221 frame so as to revolve around a loop which is formedof the plurality of video telephone/teleconference terminals and thechannels set by the channel setting device to connect the plurality ofvideo telephone/teleconference terminals. Each videotelephone/teleconference terminal also comprises a control informationtransmission device for entering control information serving to controla multipoint teleconference, into the H. 221 frame which is to berelayed by the relay device, as MLP data stipulated in CCITTRecommendation H. 221.

According to the multipoint teleconference system of the presentinvention, owing to the relay device of each videotelephone/teleconference terminal, the H. 221 frame revolves around theloop which is constituted by the plurality of videotelephone/teleconference terminals and the channels connecting them toone another. In addition, the control information for controlling themultipoint teleconference is entered into the H. 221 frame which is torevolve around the loop, as the MLP data stipulated in CCITTRecommendation H. 221, thereby permitting such control information itemsto be exchanged among the individual video telephone/teleconferenceterminals which constitute the multipoint teleconference system.Accordingly, the multipoint teleconference can be realized by only thevideo telephone/teleconference terminals which attend thisteleconference, and an MCU is not especially required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the architecture of a multipointteleconference system according to an embodiment of the presentinvention;

FIG. 2 is a block diagram showing the construction of a multipoint videotelephone/teleconference terminal in the embodiment of the presentinvention;

FIGS. 3(a) and 3(b) are explanatory views showing the operation of themultipoint teleconference system of the embodiment;

FIG. 4 is an explanatory view showing the operation of the multipointteleconference system;

FIG. 5 is an explanatory view showing the operation of the multipointteleconference system;

FIG. 6 is an explanatory diagram showing the format of a framestipulated in the CCITT Recommendation H. 221;

FIGS. 7(a) thru 7(d) are diagrams for explaining a frame stipulated inthe CCITT Recommendation H. 261, and examples of use of the frame in theembodiment of the present invention;

FIGS. 8(a) thru 8(c) are diagrams for explaining the relationships inthe embodiment between GOB's stipulated in the CCITT Recommendation H.261 and video data;

FIG. 9 is a block diagram showing the first example of construction of avideo path controller in the embodiment;

FIG. 10 is a block diagram showing the construction of a video SW/clockchange-over control in the embodiment;

FIG. 11 is a block diagram showing the construction of second example ofvideo path cotroller in the embodiment;

FIG. 12 is a block diagram showing the construction of an audioprocessor in the embodiment;

FIG. 13 is a block diagram showing an audio mean level discriminator inthe embodiment;

FIGS. 14(a) and 14(b) are explanatory diagrams showing schemes fortransmitting control information in the embodiment;

FIGS. 15(a) and 15(b) are explanatory diagrams showing schemes fortransmitting commands and data in the embodiment;

FIG. 16 is a block diagram showing the construction of the controlsystem of the chairperson terminal in the embodiment;

FIG. 17 is an explanatory diagram showing an example of display of thecontrol information in the chairperson terminal;

FIG. 18 is an explanatory diagram showing another example of display ofthe control information in the chairperson terminal;

FIG. 19 is a block diagram showing the construction of the controlsystem of the terminal other than the chairperson terminal, in theembodiment;

FIG. 20 is a block diagram showing the first example of arrangement of avideo decoder and peripheral constituents in the embodiment;

FIG. 21 is a block diagram showing the second example of arrangement ofthe video decoder and peripheral constituents in the embodiment;

FIG. 22 is an explanatory diagram showing a frame format which employsan additional channel stipulated in the CCITT Recommendation H. 221; and

FIG. 23 is a schematic diagram showing a multipoint teleconferencesystem according the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of a multipoint teleconference system according tothe present invention will be described.

First, FIG. 1 illustrates the architecture of the multipointteleconference system in this embodiment, under the assumption that thenumber of ends or terminals which attend a multipoint teleconference isfour.

Referring to the figure, numerals 1, 2, 3 and 4 indicate the ends, andnumeral 5 indicates a digital communications network. Here in thisembodiment, the end A at numeral 1 is a chairperson end which takescharge of the functions of the chairperson of the multipointteleconference. Incidentally, in this embodiment, an ISDN stipulated inthe CCITT Recommendations I-Series is assumed as the digitalcommunications network 5. Also, for the brevity of the description, itis supposed that each of the ends is connected with the ISDN by afundamental interface of 2B+D.

In this embodiment, the individual ends attending the multipointteleconference are connected in the shape of a loop. More specifically,as shown in the figure, the end-A 1 is connected to the end-D 4 and theend-B 2 by separary B channels, the end-B 2 to the end-A 1 and the end-C3, the end-C 3 to the end-B 2 and end-D 4, and the end-D 4 to the end-C3 and the end-A 1.

Next, FIG. 2 illustrates the construction of each end in thisembodiment.

Referring to the figure, the end includes a video input/output device200 such as a CRT or video camera, a video codec 201 which codes/decodesvideo information, a video path controller 202 which multiplexes/demultiplexes video information, an audio input/output device 210 suchas a loudspeaker or microphone, an audio codec 211 which codes/decodesaudio information, an audio processor 212 which processes audioinformation, a conference controller 220 which performs the controls ofvarious parts attendant upon the multipoint teleconference, a telematicunit 230, a system controller 240 which controls the entire end, anend/network signal controller 250 which performs communication controlssuch as a call control between the end and the digital communicationsnetwork 5, an MUX/DMUX (multiplexor/demultiplexor) 260 which performsthe framing process of H. 221 frames to be described later, and anetwork interface unit 270 which takes charge of the interface of alower layer with the network 5. In addition, the system controller 240is furnished with an end/end signal controller which processes controldata and notification data sent to the pertinent end or to be sent tothe other ends.

Among these constituents, the video I/O device 200, video codec 201,audio I/O device 210, audio codec 211, telematic unit 230, systemcontroller 240, end/network signal controller 250, MUX/DMUX 260, networkinterface unit 270 and end/end signal controller have the same detailsas stipulated in CCITT Recommendations H. 320, H. 221, H. 242 and H.261, and their operations in ordinary one-to-one communications are alsoas stipulated in the above recommendations. In the ensuing description,therefore, those points of difference from the ordinary one-to-onecommunications which arise in the execution of the multipointteleconference will be chiefly elucidated.

Now, the operation of the multipoint teleconference system of thisembodiment will be outlined.

FIGS. 3(a) and 3(b), FIG. 4 and FIG. 5 illustrate the situations ofvideo outputs from the video I/O devices 200 of the respective ends andaudio outputs from the audio I/O devices 210 as to the case where thefour ends A, B, C and D are holding the multipoint teleconference.

In an example depicted in FIGS. 3(a) and 3(b), all the ends presentvideo information transmitted from one of the ends, as display outputs.FIG. 3(a) shows the state in which the video information transmittedfrom the end B is presented as the display outputs by all the ends A, B,C and D. Usually, the source end of the video information is the endwhich is used by a speaker in the conference. This source end isdetermined in compliance with an instruction from the chairperson end,or it is automatically determined to be the end which is transmittingthe audio information of the highest level. FIG. 3(b) shows the state inwhich the source end of the video information has changed-over from theend B to the end C.

On the other hand, the audio outputs of the respective ends do notdepend upon the displayed video information, but they are produced bymixing all the items of audio information received from the other endsattending the conference. Herein, the audio information transmitted bythe pertinent end itself is prevented from being output in the pertinentend, by the use of an echo canceling technique.

More specifically, in the example depicted in FIGS. 3(a) and 3(b), theaudio information items transmitted from the ends B, C and D are outputby the end A; those transmitted from the ends A, C and D are output bythe end B; those transmitted from the ends A, B and D are output by theend C; and those transmitted from the ends A, B and C are output by theend D.

In an example depicted in FIG. 4, all the ends present two items ofvideo information transmitted from two different ends, as displayoutputs. FIG. 4 shows the state in which the two video information itemstransmitted from the ends A and D are respectively displayed in theupper and lower parts of the display units of all the ends A, B, C andD. Also in this case, the two source ends to transmit the displayoutputs are determined in compliance with an instruction from thechairperson end, or they are automatically determined to be the two endswhich are transmitting the audio information items of the highest leveland the second-highest level.

In the case of FIG. 4, as in the foregoing case of FIGS. 3(a) and 3(b),speech is emitted by mixing all the items of audio information receivedfrom the other ends attending the conference, irrespective of the outputvideo information items.

In an example depicted in FIG. 5, each of the ends presents the fourvideo information items of all the ends attending the teleconference, asa display output. FIG. 5 shows the state in which the video informationitems of the ends A, B, C and D are respectively displayed on thequartered areas of the screen of the display unit of each end.

In the case of FIG. 5, as in the foregoing case of FIGS. 3(a) and 3(b),speech is emitted by mixing all the items of audio information receivedfrom the other ends attending the conference, irrespective of the outputvideo information items.

In a case where five or more ends or terminals have a multipointteleconference, four source ends to transmit display outputs aredetermined in compliance with an instruction from the chairperson end,or they are automatically determined to be the four ends in the order inwhich audio information items transmitted therefrom have higher levels.

Next, there will be explained the communication frames which areemployed for the communications among the ends in this embodiment.

Here in the embodiment, the frame recommended in the provisions H. 221of the CCITT (termed "H. 221 frame" in this specification) is used forthe communication frames among the ends.

FIG. 6 illustrates the format of the H. 221 frame.

Referring to the figure, an FAS at numeral 600 is used for framesynchronization, a BAS at numeral 601 is used for transmitting acommand, an end capacity etc., and a subchannel #8 at numeral 602 isused for, for example, the transmission of an MLP message. The otherarea 603 is used for transmitting video data, audio data and user data.

The allotments of the area 603 to the video data, audio data and userdata are designated by the commands and end capacity in the BAS 601.

The multipoint teleconference system of this embodiment will be detailedbelow.

Device and expedients for realizing the video outputs of the multipointteleconference system as shown in FIGS. 3(a) and 3(b), FIG. 4 and FIG. 5will be explained under the assumed condition that the four ends orterminals A, B, C and D are connected in the loop configuration as shownin FIG. 1.

First, a transmission frame for the video data of each end will beexplained. The video data is obtained in such a way that videoinformation accepted by the video I/O device 200 is coded by, forexample, the DCT in the video codec 201. Besides, the transmission frameof the video data is entered into that part of the area 603 of the H.221 frame which is allotted to the video data.

Here in the embodiment, a frame conforming to the CCITT RecommendationH. 261 (hereinbelow, termed "H. 261 frame") is used for the transmissionframe of the video data.

FIGS. 7(a) thru 7(d) are diagrams for explaining the H. 261 frame.

FIG. 7(a) illustrates the format of the H. 261 frame.

As shown in FIG. 7(a), the H. 261 frame is comprised of a header partconsisting of a PSC 701, a TR 702, a PTYPE 703, a PEI 704 and a PSPARE705, and a data part consisting of GOB's 1˜12. The PSC 701 indicatessynchronizing data, while the TR 702 indicates the sequence No. of thecirculating system of a packet.

One picture frame is formed of the video data entered into the GOB's1˜12. That is, each of the GOB's 1˜12 contains the video data of apicture area which is obtained by dividing one picture frame by 12. Inthis regard, FIG. 8(a) shows the relationship between the GOB's 1˜12 andthe areas within the picture frame.

In the case of FIGS. 3(a) and 3(b) where the video information from oneend is output and displayed by all the ends, the source end of the videoinformation presents the video information accepted by the video I/Odevice 200, as the display output, and it generates the H. 261 frame byentering the video data into the GOB's 1˜12 and then transmits thegenerated frame. Each of the other ends receives the transmitted H. 261frame and presents the video data of the received frame as the displayoutput, and it relays and transmits the received H. 261 frame to thenext destination end. When the H. 261 frame transmitted by the sourceend has revolved through the communication channels connecting the endsand has returned to the source end itself, this source end presents thevideo data of the H. 261 frame as the display output, and it discardsdata transmitted by itself before.

FIG. 7(b) illustrates an example of use of the H. 261 frame in theforegoing case of FIG. 5 where the four video information items of allthe ends attending the teleconference are output by each end. In thisexample, the GOB's 1, 3 and 5 are allotted to the end A; those 2, 4 and6 to the end B; those 7, 9 and 11 to the end C; and those 8, 10 and 12to the end D. In this regard, FIG. 8(c) illustrates the relationshipbetween the GOB's allotted to the respective ends and the picture areasof the screen of each display unit.

Now that the end A is the chairperson end, it codes video informationaccepted at a reduction rate of 1/4 by the video I/O device 200, and itgenerates the H. 261 frame by entering the resulting video data into theGOB's 1, 3 and 5 and then transmits the generated frame. The end Breceives the H. 261 frame and presents the video information indicatedby the GOB's 1˜12 of the H. 261 frame, as the display output. Inaddition, the end B codes video information accepted at the reductionrate of 1/4 by the video I/O device 200, and it enters the new videodata of its own into the GOB's 2, 4 and 6 of the received H. 261 frameand then transmits the resulting H. 261 frame to the next destinationend.

Likewise to the end B, each of the ends C and D receives the H. 261frame and presents the video information indicated by the video data ofthe GOB's, as the display output. In addition, it codes videoinformation accepted at the reduction rate of 1/4 by the video I/Odevice 200, and it enters its own video data into the allotted GOB's ofthe received H. 261 frame and then transmits the resulting H. 261 frameto the next destination end.

When the H. 261 frame transmitted by the end A has revolved through thecommunication channels connecting the ends and has returned to the end Aitself, this end A presents the video information indicated by the videodata of the GOB's of the H. 261 frame, as the display output. Besides,the end A codes video information accepted at the reduction rate of 1/4by the video I/O device 200, it enters the new video data of its owninto the GOB's 1, 3 and 5 of the received H. 261 frame, and it transmitsthe H. 261 frame to the end B after renewing the header thereof asrequired.

In the case of FIG. 4 where the two video information items transmittedfrom the two different ends are output by each of the ends, the GOB'sare allotted to the two source ends as illustrated in FIG. 8(b). In thiscase, the ends other than the source ends perform only the operation ofdisplaying the video data items of the received H. 261 frames and theoperation of relaying the H. 261 frames. Further, in a case where theend A does not serve as the source end, it performs only the framegenerating process, the frame relaying process, and the operation ofdisplaying the video data of the H. 261 frame.

Meanwhile, FIGS. 7(c) and 7(d) illustrate different examples of use ofthe H. 261 frame in the foregoing case of FIG. 5 where the four videoinformation items of all the ends attending the teleconference areoutput by each of the ends.

The example depicted in FIG. 7(c) is such that, not only the GOB's, butalso the header is allotted to each end. Herein, each end enters its ownvideo data of the video information reduced to 1/4, into the allottedGOB's of the corresponding H. 261 frame, and it affixes only thepredetermined header into the remaining GOB's without entering any data,whereupon it transmits the resulting H. 261 frame. On the other hand,each end presents video data items contained in the GOB's allotted tothe respective ends having the corresponding H. 261 frames, as thedisplay outputs in the areas corresponding to the GOB's on the basis ofthe received H. 261 frames. In addition, when the H. 261 frametransmitted from each of the ends has revolved through the communicationchannels connecting the ends around the loop and has returned to the enditself, it enters the new video data of its own into the allotted GOB'sand renews the header of the frame as required, whereupon it transmitsthe resulting frame. Owing to such operations, one picture frame iscomprised of the four H. 261 frames.

The example depicted in FIG. 7(d) is such that, in the example of FIG.7(c), each of the ends omits the GOB's containing only the predeterminedheader information, from within the H. 261 frame.

It is controlled by the video path controller 202 (refer to FIG. 2) ofeach end to enter the video data of the end itself into the allottedGOB's of the received H. 261 frame and then relay and transmit theresulting frame as stated above.

The video path controller 202 will be detailed below.

There will be explained the first example of the video path controller202 for treating the H. 261 frame shown in FIG. 7(b) in which the GOB'sare successively allotted to the different ends.

FIG. 9 illustrates the internal construction of the video pathcontroller 202.

Also, the video codec 201 and the MUX/DMUX 260 are illustrated in thefigure.

As shown in the figure, the video codec 201 includes a video coder 910,a transmission buffer 911 and a transmission error corrector 912 as thetransmission section of the end, while it includes a reception errorcorrector 932, a reception buffer 931 and a video decoder 930 as thereception section. Besides, it includes a video codec control 920 as thecontrol section of the end.

In addition, the video path controller 202 is provided as thetransmission section of the end, and it includes a video switch 900, avideo switch clock change-over control 902 and signal delay device 901.

The MUX/DMUX 260 is supplied with the H. 261 frame of the H. 221 framereceived through the network interface 270, and it delivers the suppliedframe to the reception section of the video codec 201. Besides, theMUX/DMUX 260 generates the H. 261 frame and then generates the H. 221frame together with the other data, and it transmits the H. 221 framethrough the network interface 270.

The operation of the reception section of the end is the same as in thecase of the ordinary one-to-one communications. The video codec 201analyzes the H. 261 frame delivered from the MUX/DMUX 260 and decodesthe video data of the GOB's 1˜12, and it delivers the decodedinformation to the video I/O device 200.

The operation of the transmission section of the end is classified intothree sorts corresponding to the cases stated before; the case where theend enters the video data of its own into all the GOB's 1˜12 and thentransmits the resulting GOB's, the case where the end transmits thereceived GOB's 1˜12 as they are, and the case where the end enters thevideo data of its own into the allotted GOB's and transmits theresulting GOB's together with the received GOB's from the other sourceends.

In the case where the video codec 201 has been notified by theconference controller 220 to the effect of entering the video data ofthe pertinent end itself into all the GOB's 1˜12 and transmitting theresulting GOB's, the video coder 910 codes the video informationaccepted by the video I/O device 200 and generates the H. 261 framewhich contains the resulting video data in the GOB's 1˜12 and which isstored in the transmission buffer 911. The video SW 900 selects the data903 from the transmission buffer 911, and delivers the H. 261 frame tothe MUX/DMUX 260 through the transmission error corrector 912.

In the case where the video codec 201 has been notified by theconference controller 220 to the effect of transmitting the receivedGOB's 1˜12 as they are, the video SW 900 selects the data 904 from thereception section and delivers the received H. 261 frame to the MUX/DMUX260 through the transmission error corrector 912 without any change.

In the case where the video codec 201 has been notified by theconference controller 220 to the effect of entering the video data ofthe pertinent end itself into the allotted GOB's and transmitting theresulting GOB's together with the received GOB's of the other sourceends, the video coder 910 reduces to 1/4 the video information acceptedby the video I/O device 200 and codes the reduced information, and itgenerates the H. 261 frame which contains the resulting video data inthe GOB's allotted to the pertinent end and which is stored in thetransmission buffer 911. The allotment of the GOB's is also notified bythe conference controller 220. The video SW 900 delivers the data 903from the transmission buffer 911 of the video codec 201 and the data 905from the reception section delayed by the signal delay device 901, whilechanging them over. Herein, regarding the GOB's allotted to thepertinent end, the data 903 from the transmission buffer 911 of thevideo codec 201 is delivered to the MUX/DMUX 260 through thetransmission error corrector 912, and regarding the other GOB's and theheader of the H. 261 frame, the data 905 from the reception section isdelivered to the MUX/DMUX 260 through the transmission error corrector912. As to the chairperson end, however, regarding the GOB's allotted tothe end itself and the header of the H. 261 frame, the data 903 from thetransmission buffer 911 of the video codec 201 is delivered to theMUX/DMUX 260 through the transmission error corrector 912, and regardingthe other GOB's, the data 905 from the reception section is delivered tothe MUX/DMUX 260 through the transmission error corrector 912.

The timing of such change-over of the video SW 900 between the data 903and the data 905 is controlled by the video clock change-over control902. Incidentally, the delaying operation of the signal delay device 901is performed in order to adjust the input of the data 905 to the videoSW 900 for a time period required for the change-over control.

The change-over control of the video clock change-over control 902 forthe video SW 900 is as detailed below.

Here in this example, it is assumed that, in transmitting the H. 261frame, each end or terminal affixes header information PSC and TR as anend flag at a position directly succeeding the allotted GOB's, and thevideo clock change-over control 902 controls the changeover of the videoSW 900 on the basis of the end flag. The employment of the PSC for theend flag is based on the stipulation that the value of the PSC shall notdevelop in the video data.

Besides, in order to distinguish the PSC for the end flag from the PSC701 for the H. 261 header, the former is directly followed by a fixedvalue "11111" as the TR. Further, the most significant bit of the TR 702(5 bits) in the header of the H. 261 frame has its value fixed to "0".That is, Nos. 1 thru 15 are used as the sequence Nos. of the H. 261frames.

FIG. 10 illustrates the internal construction of the video clockchange-over control 902.

Referring to the figure, the change-over control 902 includes a dataregister 1006, an end flag detector 1001, a switch control 1002, andswitches 1005, 1003 and 1004.

In this example, owing to the video codec 201, the H. 261 frame in whichthe video data obtained by coding the video information reduced to 1/4is contained in the allotted GOB's is stored in the transmission buffer911, and the end flag composed of the PSC and the TR is entered directlybehind the allotted GOB's.

It is now assumed that the video SW 900 selects the delayed data 905from the reception section so as to deliver the selected data 905 to thetransmission error corrector 912.

On this occasion, the SW 1005 selects the data 904 from the receptionsection, and the data register 1006 as well as the end flag detector1001 monitors the end flag. When the end flag has been detected, the SWcontrol 1002 is informed of the detection. Then, the SW control 1002responsively changes-over the switches 900, 1003, 1004 and 1005. Thus,read clock pulses are sent. Consequently, the end or terminal which isnot the chairperson end reads out the data of the GOB's allotted to theend itself and the end flag affixed at the immediately succeedingposition as are stored in the transmission buffer 911. The end orterminal which is the chairperson end reads out the header part of theH. 261 frame, the data of the succeeding GOB's 1, 3 and 5 allotted tothe end itself, and the end flag affixed at the immediately succeedingposition as are stored in the transmission buffer 911.

The data 903 read out is selected by the video SW 900 in lieu of thedelayed data 905 from the reception section, and is delivered to thetransmission error corrector 912. As to the timing of the change-over ofthe video SW 900, the signal delay device 901 has its delay timeadjusted so that the start position of the data 903 may lie at the startposition of the end flag in the delayed data 905 from the receptionsection. As a result, the end flag in the delayed data 905 from thereception section disappears.

Owing to the above operation, the SW 1005 selects the data 903 from thetransmission buffer 911. Therefore, the end flag of the data 903 issubsequently monitored by the data register 1006 and the end flagdetector 1001. When the end flag has been detected, the SW control 1002is informed of the detection. Then, the SW control 1002 responsivelychanges-over the switches 900, 1003, 1004 and 1005. Consequently, theinitial state is resumed in which the delayed data 905 from thereception section is selected by the video SW 900 so as to be deliveredto the transmission error corrector 912.

With the above expedient in which each end or terminal affixes the PSCand the TR as the end flag at the position directly succeeding theallotted GOB's and then transmits the H. 261 frame, the end flaginformation items are sometimes entered into the position which containsthe GOB allotted to the next end or terminal around the loopedcommunication channels. By way of example, in the end B, the end flaginformation items are sometimes entered into the position which containsthe GOB 7 allotted to the end C. However, the data contained in the H.261 frame and transmitted by the end C has already revolved through theother ends A, B and D, and it is to be renewed into new video data bythe end C which ought to receive the H. 261 frame subsequently.Accordingly, no drawback arises.

Next, there will be explained the second example of the video pathcontroller 202 for treating the H. 261 frame shown in FIG. 7(b) in whichthe GOB's are successively allotted to the different ends or terminals.

FIG. 11 illustrates the construction of the video path controller 202 inthe second example.

Referring to the figure, the video path controller 202 includes a memory1100, a read address generator 1105 which generates the read address ofthe memory 1100, a write address generator 1104 which generates thewrite address of the memory 1100, a switch control 1103, a register1102, a GOB comparator 1101, a video switch 1106 and a buffer fortransmission 1107.

In FIG. 11, the other parts are the same as in FIG. 9 illustrative ofthe first example. In the video codec 201, the video coder 910 reducesto 1/4 the video information accepted by the video I/O device 200 andcodes the reduced video information and then enters the resulting videodata into the GOB's allotted to the pertinent end itself, therebygenerating the H. 261 frame, which is stored in the transmission buffer911.

The data 904 from the reception section is stored in the memory 1100 inaccordance with the output address of the write address generator 1104.The GOB comparator 1101 monitors the GOB of the data 904. Herein, whenthe No. of the monitored GOB indicates the GOB allotted to the pertinentend, the operation of writing the data into the memory 1101 and theoperation of incrementing the address of the write address generator1104 are suspended, and the value of the address at the time ofsuspension is stored in the register 1102. Thereafter, when the GOB No.of the data 904 has come to indicate any GOB other than the GOB'sallotted to the pertinent end, the operation of writing the data intothe memory 1101 and the operation of incrementing the address of thewrite address generator 1104 are restarted, and the data 904 is writteninto the memory 1100. The chairperson end, however, treats even theheader part of the H. 261 frame similarly to the GOB's allotted to theend itself.

On the other hand, the data stored in the memory 1100 is read out inaccordance with an address produced by the read address generator 1105,and it is sent to the transmission error corrector 912 through thetransmitting buffer 1107 by the video SW 1106. The SW control 1103compares the address value stored in the register 1102, with the valueof the output address of the read address generator 1105. When theaddress values have agreed, the operation of reading out the data fromthe memory 1100 and the operation of incrementing the address of theread address generator 1105 are suspended, and the video SW 1106 ischanged-over. Thus, the data 903 of the GOB's allotted to the pertinentend is read out of the transmission buffer 911 and is sent to thetransmission error corrector 912 through the transmitting buffer 1107.In the chairperson end, however, the header part of the H. 261 frame isalso read out and is sent to the transmission error corrector 912together with the data 903 of the allotted GOB's. Thereafter, when theoperation of reading out the data from the transmission buffer 911 hasfinished, the operation of incrementing the address of the read addressgenerator 1105 is restarted, the video SW 1106 is changed-over, and theoperation of reading out the data from the memory 1100 and then sendingit to the transmission error corrector 912 is restarted.

Incidentally, in a case where the coding operation of the video codec201 has not finished at the time of the receipt of the H. 261 frame,dummy data is entered into the allotted GOB instead of the video data.Besides, the end having received the dummy data neglects the data.

Now, there will be described devices and expedients for realizing theaudio outputs of the multipoint teleconference system illustrated inFIGS. 3(a) and 3(b), FIG. 4 and FIG. 5. Here, it is assumed that thefour ends or terminals A, B, C and D are connected in the loopconfiguration as shown in FIG. 1.

The audio data is contained in the area 603 of the H. 221 frame shown inFIG. 6.

Herein, the audio data contained in the area 603 of the H. 221 frame isobtained by mixing the audio data of all the ends which attend themultipoint teleconference. Each end receives audio data revolving aroundthe looped communication channels and cancels audio data transmitted bythe pertinent end itself before, from the received audio data, whereuponthe resulting audio data is output. In addition, each end mixes audiodata to be transmitted anew, into the aforementioned audio data obtainedin the way that the audio data transmitted by the end itself before iscanceled from the received audio data, and it transmits the resultingaudio data to the next end in the loop.

It is the audio processor 212 that realizes such operations of cancelingthe audio data transmitted by the pertinent end itself and mixing theaudio data to be transmitted anew.

The audio processor 212 will be detailed below.

FIG. 12 illustrates the internal construction of the audio processor212.

As shown in the figure, the audio processor 212 includes an echocanceler 1200 which cancels the audio data transmitted by the pertinentend itself, and a mixer 1210 which mixes the audio data to betransmitted anew.

The echo canceler 1200 includes an audio loop delay control 1201, audiovariable delay device 1202, an audio subtracter 1203, an output control1204, a linear →μ/A converter 1205, a μ/A → linear converter 1206 and anaudio level detector 1207. On the other hand, the mixer 1210 includes aμ/A → linear converter 1211, an audio adder 1212, a linear →μ/Aconverter 1213 and an audio mean level discriminator 1214.

In the echo canceler 1200, the audio loop delay control 1201 is notifiedof a delay time taken since the transmission of the audio data till thereturn thereof to the pertinent end after having revolved around theloop, by the system controller 240, and it sets the delay time in theaudio variable delay device 1202. As the delay time, a time period inwhich a specified transmitted H. 221 frame returns to the pertinent endafter its revolution around the loop is measured in the MUX/DMUX 260,and it is reported to the system controller 240.

The μ/A → linear converter 1211 converts audio data coded in accordancewith the μ/A rules by the audio codec 211, back into linear data, and itsends the linear data to the audio variable delay device 1202. The audiovariable delay device 1202 delays the audio data delivered from the μ/A→ linear converter 1211, for the set time period, and it delivers thedelayed data to the audio subtracter 1203.

On the other hand, the MUX/DMUX 260 extracts audio data from within thereceived H. 221 frame, and it sends the audio data to the μ/A → linearconverter 1206. This, μ/A → linear converter 1206 converts the audiodata coded in accordance with the μ/A rules and delivered from theMUX/DMUX 260, back into linear data, and it delivers the linear data tothe audio subtracter 1203.

The audio subtracter 1203 subtracts the output audio data of the audiovariable delay device 1202 from that of the μ/A → linear converter 1206.Thus, the audio data transmitted by the pertinent end before is canceledfrom the received audio data.

The audio data after such cancellation is delivered to the linear →μ/Aconverter 1205 through the output control 1204 and is coded inaccordance with the μ/A rules by the converter 1205, whereupon the codeddata is sent to the audio codec 211. This audio codec 211 decodes thedelivered audio data, and supplies the decoded data to the audio I/Odevice 210.

In addition, the audio data, which has been obtained in the way that theaudio data transmitted by the pertinent end before is canceled fromwithin the received audio data, is sent to the audio adder 1212 throughthe output control 1204. The audio adder 1212 adds up the audio datasent from the output control 1204 and audio data delivered from the μ/A→ linear converter 1211. Thus, the audio data to be transmitted anew ismixed. Therefore, the linear →μ/A converter 1213 codes the resultingaudio data in accordance with the μ/A rules and sends the μ/A-coded datato the MUX/DMUX 260. This MUX/DMUX 260 enters the sent audio data intothe H. 221 frame, and transmits the resulting frame to the next end inthe loop.

The audio mean level discriminator 1214 calculates the level of theaudio data delivered from the m/A linear converter 1211, and sends thecalculated level to the conference controller 220. The discriminatedlevel of the audio data is used for the automatic change-over of thevideo data items to be displayed on the basis of the sound volumes ofaudio data items as stated before.

Further, the audio level detector 1207 operates when the pertinent endis the chairperson end. This detector 1207 notifies the conferencecontroller 220 of the level of the audio data obtained in the way thatthe audio data transmitted by the pertinent end before is canceled fromwithin the received audio data. Besides, the output control 1204 is adevice for bringing the output value of the audio data of the echocanceler 1200 to zero once in compliance with an instruction from theconference controller 220. Incidentally, in this embodiment, the audiocodec 211 is supposed to be a readymade one which is interfaced with thedata coded in accordance with the μ/A rules. However, in a case wherethe audio codec 211 is one interfaced with linear data, the μ/A → linearconverter 1211 and the linear →μ/A converter 1205 are dispensed with.

Here, the details of the audio mean level discriminator 1214 will beexplained.

FIG. 13 illustrates the internal construction of the audio mean leveldiscriminator 1214.

As shown in the figure, the audio mean level discriminator 1214 includesan audio adder 1301, a write control 1302, a memory 1303, a counter1304, a counter value comparator 1305, a reset control 1306, adiscrimination control 1307 and an audio level discriminator 1308.

When supplied with the audio data from the μ/A → linear converter 1211,the audio adder 1301 reads out the value of the addition of the audiodata items up to the last audio data, from the memory 1303, and it addsup the read-out value and the output audio data of the μ/A → linearconverter 1211. Subsequently, it writes the audio data after theaddition into the memory 1303 through the write control 1302. The numberof times of writing into the memory 1303 is counted by the counter 1304.

When the number of times of writing into the memory 1303 is decided tohave reached a predetermined number by the comparator 1305, thediscrimination control 1307 notifies the audio level discriminator 1308and the reset control 1306 of the decided situation. Upon thenotification, the audio level discriminator 1308 reads out the additionvalue of the audio data stored till then, from the memory 1303, and itinforms the conference controller 220 of the read-out value.

On the other hand, the reset control 1306 notified of the situation ofthe writing resets the content of the memory 1303 and the count value ofthe counter 1304.

In the above, the details of the multipoint teleconference systemconcerning the video data and the audio data have been explained.

Now, the details of the multipoint teleconference system will beexplained in relation to controls required for holding and managing themultipoint teleconference.

In this embodiment, it is realized by exchanging control informationamong the chairperson end and the other ends to construct the multipointteleconference system in which the ends are connected in the loopconfiguration as described before in conjunction with FIG. 1, to alterthe construction of the multipoint teleconference system on account ofany end leaving the multipoint teleconference, to designate video datato be presented as a display output in each end, and so forth.

First, the transmission frame of the control information will beexplained.

In this embodiment, for the purpose of transmitting the controlinformation, the area of the MLP data stipulated in CCITT RecommendationH. 221 is secured in, the subchannel #8 (at numeral 602) of the H. 221frame shown in FIG. 6, and a plurality of channels lying in this areaare respectively assigned to the different ends. Thus, each endtransmits the control information using the assigned channel.

Each of FIGS. 14(a) and 14(b) illustrates the channels in the MLP dataarea.

The MLP data area has a size of 6.4 kb/s or 4 kb/s, and it can besecured by a command in the BAS area (at numeral 601 in FIG. 6).

Shown in FIG. 14(a) is a case where the MLP data area is secured withthe size of 6.4 kb/s. In this case, the eight channels of a commonchannel and channels Nos. 1˜7 are defined in 8-bit unit in the MLP dataarea as seen from the figure. Therefore, the common channel is used forthe chairperson end, and the other channels are assigned to the otherends by the control information of the common channel.

Shown in FIG. 14(b) is a case where the MLP data area is secured withthe size of 4 kb/s. In this case, the five channels of a common channeland channels Nos. 1˜4 are defined in 8-bit unit in the MLP data area asseen from the figure. Therefore, the common channel is used for thechairperson end, and the other channels are assigned to the other endsby the control information of the common channel.

Incidentally, the BAS area may well be employed for the transmission ofthe control information instead of the MLP data area.

More specifically, the BAS area 601 of the H. 221 frame shown in FIG. 6may Awell be extended into the subchannel #8 (at numeral 602) by thecommand of the BAS area 601, so as to use the extended part of this areafor transmitting the control information items of the individual ends.

The control information to be transmitted by each channel consists of acommand and data.

The command and the data to be transmitted may well be entered into thechannel of the identical H. 221 frame as illustrated in FIG. 15(a).Alternatively, they may well be dividedly entered into the channels ofthe successive H. 221 frames as illustrated in FIG. 15 (b).

With any of such transmitting schemes, each of the ends analyzes the MLPdata area or BAS area of the received H. 221 frame. It extracts orcancels the control information transmitted by the pertinent end itselfbefore and contained in the channel assigned thereto, and it relays thecontrol information items in the other channels of the MLP data area orBAS area of the received H. 221 frame than the channel assigned to thepertinent end, to the next end in the loop without any change.

In the presence of new control information to be transmitted, each endenters the information into the channel assigned to the pertinent enditself, and it transmits the new control information to the next end inthe loop, together with the control information items in the otherchannels of the MLP data area or BAS area of the received H. 221 framethan the channel assigned to the pertinent end.

The multipoint teleconference employing the control information itemswhich are exchanged among the chairperson end and the other ends,proceed as detailed below.

The multipoint teleconference system employing the control informationitems is controlled principally by the system controllers 240 andconference controllers 220 of the respective ends.

First, the details of the system controller 240 and conferencecontroller 220 of the chairperson end will be explained.

FIG. 16 illustrates that control processing of the multipointteleconference which is peculiar to the end serving as the chairperson.In this embodiment, each of the ends is endowed with functions foroperating as the chairperson end.

The teleconference which utilizes the looped teleconference system shownin FIG. 1, is started as follows:

On this occasion, when the system controller 240 of the chairperson endA has the other conferee ends B, C and D designated from an unshownkeyboard, it controls the end/network controller 250 so as to establisha call between the end A and the end B. subsequently, a callorigination/clearing process 1613 supplies a packet composing/sendingcontrol process 1627 with a command for instructing the called end B toconnect with the end C. The packet composing/sending control process1627 enters the supplied command into the common channel to generate MLPdata or BAS data, which is subjected to an MUX interface process 1629and is thereafter delivered to the MUX/DMUX 260. The MUX/DMUX 260generates the H. 221 frame containing the delivered MLP data or BASdata, and the generated frame is transmitted to the end B through thenetwork interface 270.

When the end B has connected with the end C, the system controller 240of the chairperson end A transmits, to the end C, a command forinstructing the end C to connect with the end D. The command is sentthrough the end B. Thereafter, when the end C has connected with the endD, the system controller 240 transmits a command, to the end D, forinstructing the end D to connect with the end A. This command is sentthrough the ends B and C. When the ends A and D have connected, thelooped system is entirely constructed.

In this manner, the ends to attend the teleconference are successivelyconnected by the commands for instructing the connections with theadjacent ends, whereby the loop is formed up.

Next, the audio control in the multipoint teleconference will beexplained.

The conference controller 220 decides whether or not the level reportedby the audio level detector 1207 (refer to FIG. 12) of the audioprocessor 212 is a mute level for a predetermined time period, in otherwords, whether or not it is below the predetermined level judged to bemute, for the predetermined time period (1621). Herein, subject to themute level for the predetermined time period, the conference controller220 instructs the output control 1204 of the audio processor 212 totemporarily bring the audio data to "0", whereby the audio output of theecho canceler 1200 is temporarily turned OFF (1620).

When the audio data level is reset in this manner, calculation errorswhich develop in the audio subtracter 1203 and audio adder 1212 of theaudio processor 212 are restrained from accumulating in the audio data.Incidentally, the accumulation of the calculation errors arises as noisein the case of outputting the audio data.

Next, the change-over control of video data to be displayed in the endswill be explained.

In this embodiment, the automatic mode based on the audio data levels ofthe individual ends or the manual mode based on a change-over requestmade by any of the ends can be selected for the change-over control ofthe video data. The selection is effected with an auto/manualchange-over switch 1625.

There will be explained the case where the video data items areautomatically changed-over on the basis of the audio data levels of theends.

The MUX/DMUX 260 delivers the MLP data or BAS data contained in thereceived H. 221 frame, to a packet decomposing/sending control process1628 through a DMUX interface process 1630. The packetdecomposing/sending control process 1628 decodes the delivered MLP dataor BAS data, and supplies a memory Awrite control 1622 with the dataitems of the audio mean levels sent from the individual ends. The memorywrite control 1622 writes the data items of the respective ends into amemory 1623, the levels are compared by a comparison process 1624, and avideo path change-over instruction process 1626 is notified of the endwhich exhibits the highest audio data level. Subsequently, the videopath change-over instruction process 1626 supplies the packetcomposing/sending control process 1627 with a command for turning thevideo data to-be-displayed into the video data of the end of the highestaudio data level. The packet composing/sending control process 1627generates MLP data or BAS data containing the command in the commonchannel, and the generated data is subjected to the MUX interfaceprocess 1629 and is delivered to the MUX/DMUX 260. Then, the MUX/DMUX260 generates an H. 221 frame containing the delivered MLP data or BASdata, so as to transmit the frame to the ends in the loop through thenetwork interface 270.

Next, there will be explained the case where the video data items to bepresented as the display outputs in the ends are changed-over on thebasis of the change-over request made by any of the ends.

The MUX/DMUX 260 delivers the MLP data or BAS data contained in thereceived H. 221 frame, to the packet decomposing/sending control process1628 through the DMUX interface process 1630. The packet decomposing/sending control process 1628 decodes the delivered MLP data or BAS data,and supplies a change-over request process 1611 with a change-overrequest command if this command is contained. When the change-overrequest process 1611 is supplied with the command indicative of thechange-over request, or when an instruction for the change-over requestis given from the keyboard, the content of the change-over request isdelivered to a character superposition process 1603. Then, the charactersuperposition process 1603 produces characters to-be-superposed anddelivers them to a screen display process 1604, which presents thecontent of the change-over request in superposition on the displayoutput picture of the video I/O device 200 as shown in FIG. 17.

Subsequently, a request input process 1610 notifies the video pathchange-over instruction process 1626 of the end which is transmittingthe video data requested to be displayed by the change-over request. Thevideo path change-over instruction process 1626 supplies the packetcomposing/sending control process 1627 with a command for turning thevideo data to-be-displayed into the video data of the aforementionedend. The packet composing/sending control process 1627 generates MLPdata or BAS data containing the command in the common channel, and thegenerated data is subjected to the MUX interface process 1629 and isdelivered to the MUX/DMUX 260. Then, the MUX/DMUX 260 generates an H.221 frame containing the delivered MLP data or BAS data, so as totransmit the frame to the ends in the loop through the network interface270.

Next, there will be explained a case where any of the ends leaves theteleconference utilizing the looped teleconference system shown in FIG.1, in the course of this teleconference, or a case where a new endattends the teleconference midway.

The MUX/DMUX 260 delivers the MLP data or BAS data contained in thereceived H. 221 frame, to the packet decomposing/sending control process1628 through the DMUX interface process 1630. The packet decomposing/sending control process 1628 decodes the delivered MLP data or BAS data,and supplies a leaving/attendance process 1614 with a leaving requestcommand if this command is contained. When the leaving/attendanceprocess 1614 is supplied with the leaving request command, or when aninstruction for a leaving request or an attendance request is given fromthe keyboard, the content of the request is delivered to a charactersuperposition process 1601. Then, the character superposition process1601 produces characters to-be-superposed and delivers them to a screendisplay process 1602, which presents the content of the request insuperposition on the display output picture of the video I/O device 200as shown in FIG. 18.

Subsequently, a request input/sole input process 1612 notifies the callorigination/clearing control process 1613 of the content of the request.The call origination/clearing control process 1613 generates clearingcommands and call origination commands in dependence on the content ofthe request, and delivers them to the packet composing/sending controlprocess 1627. The clearing command instructs the two ends which are eachadjoining the end which is leaving in the loop to cut off theirconnections with the leaving end, or it instructs the end to attend todisconnect the two ends connected in the loop and lying near it. On theother hand, the call origination command instructs the connectionbetween the ends which previously connected with the end having justleft, or it instructs the formation of a loop which includes the end toattend. More specifically, in a case where the end C in FIG. 1 requeststo leave the teleconference, the disconnection between the ends C and Dis instructed by the clearing command, the disconnection between theends C and B is instructed by the clearing command, and the connectionof the end B with the end D is instructed by the call originationcommand. Further, in a case where the end E to attend the teleconferenceanew is inserted between the ends B and C in FIG. 1, the disconnectionbetween the ends B and C is instructed by the clearing command, theconnection of the end B with the end E is instructed by the callorigination command, and the connection of the end E with the end C isinstructed by the call origination command after the end E has connectedwith the end B.

The packet composing/sending control process 1627 generates MLP data orBAS data in which the command delivered from the callorigination/clearing control process 1613 is contained in the commonchannel. The generated data is subjected to the MUX interface process1629 and is delivered to the MUX/DMUX 260. Then, the MUX/DMUX 260generates an H. 221 frame containing the delivered MLP data or BAS data,so as to transmit the frame to the ends in the loop through the networkinterface 270.

Next, there will be explained the control processing of the multipointteleconference by the end which is not the chairperson end.

FIG. 19 illustrates the control processing of the multipointteleconference by the end other than the chairperson end.

First, let's consider a case where the pertinent end has been instructedby the chairperson end to connect with or disconnect from any other end.

The MUX/DMUX 260 delivers the MLP data or BAS data contained in thereceived H. 221 frame, to an unshown packet decomposing/sending controlprocess through a DMUX interface process 1909. The packet decomposing/sending control process decodes the delivered MLP data or BAS data, andsupplies the system controller 240 with a call origination command or aclearing command if this command is contained in the common channel(refer to FIGS. 14(a) and 14(b)). The system controller 240 controls theend/network controller 250 so as to connect or disconnect the pertinentend with or from the end designated by the command.

Secondly, let's consider a case where the pertinent end has beeninstructed by the chairperson end to change-over video datato-be-displayed.

The MUX/DMUX 260 delivers the MLP data or BAS data contained in thereceived H. 221 frame, to the unshown packet decomposing/sending controlprocess through the DMUX interface process 1909. The packet decomposing/sending control process decodes the delivered MLP data or BAS data, andsupplies the main conferential control process 1907 of the conferencecontroller 220 with a command instructive of the change-over of thevideo data to-be-displayed if this command is contained in the commonchannel.

In accordance with the content of the supplied command, the mainconferential control process 1907 of the conference controller 220determines if the video data of the pertinent end is to be entered intothe H. 261 frame which is to be transmitted from this end. In case oftransmitting the H. 261 frame which contains the video data of thepertinent end, the main conferential control process 1907 determines thesize of video information to be sent by the pertinent end and the GOB'sto contain the video data. Further, the control process 1907 notifiesthe video codec 201 and the video path controller 202 of the determinedcontents. As stated before, the video codec 201 and the video pathcontroller 202 operate on the basis of the notification.

Next, there will be explained processing for transmitting the audio meanlevel to the chairperson end.

When the main conferential control process 1907 of the conferencecontroller 220 is notified of the audio mean level by the audio meanlevel discriminator 1214 of the audio processor 212 as stated before, itdelivers the data of the level to an unshown packet composing/ sendingcontrol process. The packet composing/sending control process generatesMLP data or BAS data containing the data in the channel assigned to thepertinent end, and the generated data is subjected to an MUX interfaceprocess 1908 and is delivered to the MUX/DMUX 260. Then, the MUX/DMUX260 generates an H. 221 frame containing the delivered MLP data or BASdata, so as to transmit the frame to the chairperson end in the loopthrough the network interface 270.

Next, there will be explained processing by which the request forchanging-over the video data, the request for leaving the teleconferencemidway or a request for transmitting telematic end data is transmittedto the chairperson end.

When such a request is input to the pertinent end from the keyboard orthe like not shown, the input accepting process 1903 of the systemcontroller 240 accepts the request and delivers it to the main control1906 thereof. The main control 1906 generates a command conforming tothe delivered request, and delivers the command to the main conferentialcontrol process 1907. This control process 1907 delivers the command tothe packet composing/sending control process not shown. The packetcomposing/sending control process generates MLP data or BAS datacontaining the command in the channel assigned to the pertinent end, andthe generated data is subjected to the MUX interface process 1908 and isdelivered to the MUX/DMUX 260. Then, the MUX/DMUX 260 generates an H.221 frame containing the delivered MLP data or BAS data, so as totransmit the frame to the chairperson end in the loop through thenetwork interface 270.

Incidentally, a character superposition process 1905 superposes thecommand, the data etc. received from the chairperson end, on the displayof the screen of the video I/O device 200 (a screen display process1904) under the control of the main control 1906.

Meanwhile, the above embodiment has mentioned the expedient (FIGS.7(a)˜7(d)) in which the video data items transmitted by the four endsare contained in the H. 261 frame.

The video codec 201 of each end decodes the video data contained in thereceived H. 261 frame, and presents the display output on the video I/Odevice 200.

In this regard, in the case where the video data items transmitted bythe four ends are contained in the H. 261 frame, they are independent ofone another. Therefore, the video codec 201 can treat the video dataitems transmitted by the respective ends, independently of one another.

In this embodiment, accordingly, the video codec 201 of each endpresents the decoded video data as the display output when the decodingof the video data transmitted by the individual end has finished.

FIG. 20 illustrates the arrangement of the video decoder and peripheralconstituents in the video codec 201.

Referring to the figure, numeral 2005 indicates the decoder, numeral2001 a decoding memory, numerals 2000 and 2007 a display memory ofdouble buffer construction, and numeral 2008 a reception memory. Thevideo I/O device 200 is connected with the buffer of the display memorythrough a switch 2003. When one of the buffers 2000 and 2007 operatesfor writing decoded data, the other operates for reading out data to bedisplayed by the video I/O device 200.

The decoder 2005 reads out received video data from the reception memory2008, and decodes it by reference to the decoded data of the last framestored in the decoding memory 2001. The decoded data is written into thedecoding memory 2001 so as to be referred to in the operation ofdecoding the next frame, and it is also written into the buffer 2000 ofthe display memory currently operating for writing the decoded data.When the video data corresponding to 1/4 picture area as transmitted byone end has been decoded, the buffers 2000 and 2007 are changed-over soas to use the former for reading out the data to-be-displayed and to usethe latter for writing the decoded data.

In this regard, a single memory can be shared for the display memory andthe decoding memory.

FIG. 21 illustrates an arrangement in the case of using the singlememory for both the display memory and the decoding memory.

Referring to the figure, numeral 2105 indicates a decoder, numerals 2101and 2102 a memory of double buffer construction which is used as boththe decoding memory and the display memory, and numeral 2008 a receptionmemory. The video I/O device 200 is connected with the decoding/displaymemory through a switch 2104. When one of the buffers 2101 and 2102 ofthe decoding/display memory operates as the decoding memory for readingout reference data and the display memory for reading out datato-be-displayed, the other buffer operates as the decoding memory forwriting decoded data and the display memory.

The decoder 2105 reads out received video data from the reception memory2008, and decodes it by reference to the decoded data of the last frameread out of the buffer 2101 which is operating as the decoding memoryfor reading out the reference data. In parallel with the operation ofreading out the reference data from the buffer 2101, the decoded data ofthe buffer 2101 is read out for display and is sent to the video I/Odevice 200. The data decoded by the decoder 2105 is written into thebuffer 2102 operating as the decoding memory for weriting the decodeddata, so as to be referred to in the operation of decoding the nextframe. When the video data corresponding to 1/4 picture area astransmitted by one end has been decoded, the decoded data of an areaother than the 1/4 area having been processed this time is transferredto the buffer 2102 from the buffer 2101 operating as the decoding memoryfor reading out the reference data, and the roles of the buffers 2101and 2102 are changed-over.

Thenceforth, likewise to the above, each time the video datacorresponding to 1/4 picture area as transmitted by one end has beendecoded, it is transferred to the buffer 2102, and the roles of thebuffers 2101 and 2102 are changed-over.

In the foregoing embodiment, the looped multipoint teleconference systemis constructed in such a way that the pertinent end is connected witheach of the adjacent ends by the single B channel as illustrated in FIG.1.

Since, however, the single B channel consists of two transfer paths ofopposite transmitting directions, two looped communication channels areactually formed in the case of connecting the pertinent end with each ofthe adjacent ends by the single B channel. In the above, there has beendescribed the case where only one of the two looped communicationchannels is used. In this regard, the communication capacity among theends can be increased by simultaneously using the two loopedcommunication channels. By way of example, video data and audio data canbe distributed to the tatwo looped communication channels in such amanner that the former is transmitted by the H. 221 frame of one ofthese communication channels, while the latter is transmitted by the H.221 frame of the other communication channel.

Moreover, in this case, the H. 221 frame can be extended by utilizing anH. 221 frame shown in FIG. 22 as employs the additional channelstipulated in the CCITT Recommendation H. 221. That is, one of the twolooped communication channels is used as the "first channel" in theRecommendation H. 221, while the other communication channel is used asthe "additional channel" in the same.

The looped multipoint teleconference system of the foregoing embodimentis constructed by connecting the pertinent end with each of the adjacentends by the single B channel as illustrated in FIG. 1. Since, however,the single B channel consists of the two transfer paths of the oppositetransmitting directions as stated before, even an architecture shown inFIG. 23 in which the pertinent end is connected with the succeeding endby the single B channel can form looped communication channels. Morespecifically, the ends or terminals 1 and 2 lying at both theextremities of the system architecture fold back and transmit H. 221frames. The ends or terminals 3 and 4 not lying at the extremitiestransmit received H. 221 frames to the next ends in penetrating fashionin either transmitting direction. The present invention is similarlyapplicable to the case of forming the looped communication channels inthis manner.

In the above embodiments, the ISDN stipulated in the CCITTRecommendations I-series is assumed as the digital communicationsnetwork 5 shown in FIG. 1, and each end is assumed to be connected withthe ISDN by the fundamental interface of 2B+D.

However, the present invention is not restricted to the connection withthe ISDN by the fundamental interface of 2B+D, but it is similarlyapplicable to a case where each end is connected with the ISDN by afirst-order group velocity interface. Besides, when a plurality of Bchannels within the first-order group velocity interface is employed inthis case, the H. 221 employing the additional channel can be used.

As set forth above, according to the present invention, it is possibleto provide a multipoint teleconference system in which a multipointteleconference can be realized by only conferee ends without requiringan MCU.

What is claimed is:
 1. An end terminal in a teleconferencing system forcommunicating data along a network, said end terminal comprising:aninterface unit for receiving a first communication frame from saidnetwork, said first communication frame having a predetermined number ofsections for storing, respectively, video data from a predeterminednumber of end terminals in said teleconferencing system; a display unitfor displaying the video data stored in said predetermined number ofsections of said communication frame; a video input circuit foracquiring video data; a video replacement circuit for replacing videodata in one of said predetermined number of sections of said firstcommunication frame with the video data acquired by said video inputcircuit to generate a second communication frame; and a transmitter fortransmitting said second communication frame to said network.
 2. The endterminal recited in claim 1, wherein said video replacement circuitincludes:a video path controller for receiving the video data from saidvideo input circuit and the video data in said predetermined number ofsections of the first communication frame, said video path controllerincluding a switching circuit for outputting the video data from saidvideo input circuit and the video data in all of said predeterminednumber of sections of the first communication frame except said one ofsaid predetermined number of sections of said first communicationsframe; and a multiplexer for combining the video data output from saidswitching circuit to form said second communication frame.
 3. The endterminal recited in claim 2, wherein said video path controller furtherincludes:a delay circuit for delaying switching of the video data in allof said predetermined number of sections of the first communicationframe except said one of said predetermined number of sections for atime sufficient to enable formation of said second communication frameby said multiplexer.
 4. The end terminal recited in claim 3, whereinsaid video replacement circuit further includes:a video clockchange-over controller for generating timing signals for controlling theswitching performed by said switching circuit.
 5. The end terminalrecited in claim 1, wherein said transmitter transmits said secondcommunication frame to said interface unit for output to said network.6. The end terminal recited in claim 1, wherein said display unitdisplays the video data stored in said predetermined number of sectionsof said first communication frame simultaneously.
 7. The end terminalrecited in claim 1,wherein said interface unit receives a thirdcommunication frame having predetermined number of sections for storing,respectively, audio data from a predetermined number of end terminals insaid teleconferencing system, and wherein said end terminal furthercomprises: an audio output circuit for audibly presenting the audio datain said predetermined number of sections of said third communicationframe; an audio input circuit for acquiring audio data; and an audioreplacement circuit for replacing audio data in one of saidpredetermined number of sections of said third communication frame withthe audio data acquired by said audio input circuit to generate a fourthcommunication frame, said transmitter transmitting said fourthcommunication frame to said network.
 8. The end terminal recited inclaim 7, wherein said first communication frame and said thirdcommunication frame form respective portions of a single communicationframe received by said interface unit.
 9. The end terminal recited inclaim 8, further comprising:a multiplexer, coupled to said interfaceunit, for inputting the video data in said predetermined number ofsections of said first communication frame into said video replacementcircuit and for inputting the audio data in said predetermined number ofsections of said third communication frame into said audio replacementcircuit.
 10. The end terminal recited in claim 7, wherein said secondcommunication frame and said fourth communication frame form respectiveportions of a single communication frame to be transmitted by saidtransmitter.
 11. The end terminal recited in claim 7, wherein said audiodata being replaced by said audio replacement circuit is audio datapreviously transmitted by said end terminal.
 12. The end terminalrecited in claim 11, wherein said audio replacement circuit includes:anecho canceller for cancelling the audio data in said one of saidpredetermined number of sections of said third communication frame; anda mixer for inserting the audio data acquired by said audio input/outputunit into said one of said predetermined sections of said thirdcommunication frame, to thereby form said fourth communication frame.13. An end terminal in a teleconferencing system for communicating dataalong a network, said end terminal receiving from said network a firstcommunication frame having a predetermined number of sections forstoring video data from respective ones of a predetermined number of endterminals in said teleconferencing system, said end terminalcomprising:a display for displaying the video data stored in at leastone of said predetermined number of sections of said first communicationframe; a video input circuit for acquiring video data; a videoreplacement circuit for replacing video data in one of saidpredetermined number of sections of said first communication frame withthe video data acquired by said video input unit to form a first updatedcommunication frame; and a transmitter for transmitting said firstupdated communication frame to said network.
 14. The end terminalrecited in claim 13, wherein said display displays the video stored allof said predetermined number of sections of said first communicationframe simultaneously.
 15. The end terminal recited in claim 13, whereinsaid video replacement circuit includes:a video path controller forreceiving the video data from said video input circuit and the videodata in said predetermined number of sections of the first communicationframe, said video path controller including a switching circuit foroutputting the video data from said video input circuit and the videodata in all of said predetermined number of sections of the firstcommunication frame except said one of said predetermined number ofsections; and a multiplexer for combining the video data output fromsaid switching circuit to form said first updated communication frame.16. The end terminal recited in claim 15, wherein said video pathcontroller includes a delay circuit for delaying switching of the videodata in all of said predetermined number of sections of the firstcommunication frame except said one of said predetermined number ofsections for a time sufficient to enable formation of said first updatedcommunication frame by said multiplexer.
 17. The end terminal recited inclaim 16, wherein said video replacement circuit further comprises:avideo clock change-over controller for generating timing signals forcontrolling the switching performed by said switching circuit.
 18. Theend terminal recited in claim 13, further comprising:an interface unitfor receiving a second communication frame having predetermined numberof sections for storing, respectively, audio data from a predeterminednumber of end terminals in said teleconferencing system, and whereinsaid end terminal further comprises: an audio output circuit for audiblypresenting the audio data in said predetermined number of sections ofsaid second communication frame; an audio input circuit for acquiringaudio data; and an audio replacement circuit for replacing audio data inone of said predetermined number of sections of said secondcommunication frame with the audio data acquired by said audio inputcircuit to generate a second updated communication frame, saidtransmitter transmitting said second updated communication frame to saidnetwork.
 19. The end terminal recited in claim 18, wherein said firstcommunication frame and said second communication frame form respectiveportions of a single communication frame received by said interfaceunit.
 20. The end terminal recited in claim 19, further comprising:amultiplexer, coupled to said interface unit, for inputting the videodata in said predetermined number of sections of said firstcommunication frame into said video replacement circuit and forinputting the audio data in said predetermined number of sections ofsaid second communication frame into said audio replacement circuit. 21.The end terminal recited in claim 18, wherein said first updatedcommunication frame and said second updated communication frame formrespective portions of a single communication frame to be transmitted bysaid transmitter.
 22. The end terminal recited in claim 18, wherein saidaudio data being replaced by said audio replacement circuit is audiodata previously transmitted by said end terminal.
 23. The end terminalrecited in claim 22, wherein said audio replacement circuit includes:anecho canceller for cancelling the audio data in said one of saidpredetermined number of sections of said second communication frame; anda mixer for inserting the audio data acquired by said audio input unitinto said one of said predetermined sections of said secondcommunication frame, to thereby form said second updated communicationframe.
 24. A teleconferencing system for communicating video informationamong a plurality of terminals connected to a network, said systemcomprising:a first terminal for transmitting a first communication frameto said network, said first communication frame having a predeterminednumber of sections for storing video data from respective ones of apredetermined number of said plurality of terminals; and a secondterminal including:an interface unit for receiving the firstcommunication frame transmitted by said first terminal, a display fordisplaying the video data stored in at least one of said predeterminednumber of sections of the first communication frame, a video inputcircuit for acquiring video data, a video replacement circuit forreplacing video data in one of said predetermined number of sections ofthe first communication frame with the video data acquired by said videoinput circuit to generate a first updated communication frame, and atransmitter for transmitting said first updated communication frame toone of said plurality of terminals.
 25. The teleconferencing systemrecited in claim 24, wherein said video replacement circuit includes:avideo path controller for receiving the video data from said video inputcircuit and the video data in said predetermined number of sections ofthe first communication frame, said video path controller including aswitching circuit for outputting the video data from said video inputcircuit and the video data in all of said predetermined number ofsections of the first communication frame except said one of saidpredetermined number of sections; and a multiplexer for combining thevideo data from said video input circuit with the video data in all ofsaid predetermined number of sections of the first communication frameexcept said one of said predetermined number of sections to form saidfirst updated communication frame.
 26. The teleconferencing systemrecited in claim 25, wherein said video path controller includes a delayfor delaying switching of the video data in all of said predeterminednumber of sections of the first communication frame except said one ofsaid predetermined number of sections for a time sufficient to enableformation of said first updated communication frame by said multiplexer.27. The teleconferencing system recited in claim 26, wherein said videoreplacement circuit further includes:a video clock change-overcontroller for generating timing signals for controlling the switchingperformed by said switching circuit.
 28. The teleconferencing systemrecited in claim 27, wherein said display displays the video data storedin all of said predetermined number of sections of said firstcommunication frame simultaneously.
 29. The teleconferencing systemrecited in claim 24, wherein said second terminal receives a secondcommunication frame having predetermined number of sections for storing,respectively, audio data from a predetermined number of said pluralityof terminals, said second terminal further including:an audio outputcircuit for audibly presenting the audio data in said predeterminednumber of sections of said second communication frame; an audio inputcircuit for acquiring audio data; and an audio replacement circuit forreplacing audio data in one of said predetermined number of sections ofsaid second communication frame with the audio data acquired by saidaudio input circuit to generate a second updated communication frame,said transmitter transmitting said second updated communication frame tosaid network.
 30. The teleconferencing system recited in claim 29,wherein said first communication frame and said second communicationframe form respective portions of a single communication frame receivedby said interface unit.
 31. The teleconferencing system recited in claim30, wherein said second terminal further includes:a multiplexer, coupledto said interface circuit, for inputting the video data in saidpredetermined number of sections of said first communication frame intosaid video replacement circuit and for inputting the audio data in saidpredetermined number of sections of said second communication frame intosaid audio replacement circuit.
 32. The end terminal recited in claim29, wherein said first updated communication frame and said secondupdated communication frame form respective portions of a singlecommunication frame to be transmitted by said transmitter.
 33. The endterminal recited in claim 29, wherein said audio data being replaced bysaid audio replacement circuit is audio data previously transmitted bysaid end terminal.
 34. The end terminal recited in claim 29, whereinsaid audio replacement circuit includes:an echo canceller for cancellingthe audio data in said one of said predetermined number of sections ofsaid second communication frame; and a mixer for inserting the audiodata acquired by said audio input unit into said one of saidpredetermined sections of said second communication frame, to therebyform said second updated communication frame.
 35. A method forcommunicating data within a teleconferencing system containing aplurality of end terminals connected to a network, said methodcomprising the steps of:receiving, at one end terminal, a firstcommunication frame from said network, said first communication framehaving a predetermined number of sections for storing video data fromrespective ones of a predetermined number of said plurality of endterminals; displaying the video data stored in at least one of saidpredetermined number of sections of said first communication frame;obtaining video data at said one end terminal; replacing the video datain one of said predetermined number of sections of said firstcommunication frame with the video data obtained at said one endterminal to generate a first updated communication frame; andtransmitting said first updated communication frame to said network. 36.The method of claim 35, further comprising the steps of:displaying thevideo stored all of said predetermined number of sections of said firstcommunication frame simultaneously.
 37. The method of claim 35, whereinsaid replacing step comprises the step of:multiplexing the video dataobtained from said one end terminal and the video data in all of saidpredetermined number of sections of the first communication frame exceptsaid one of said predetermined number of sections to form said firstupdated communication frame.
 38. The method of claim 37, wherein saidmultiplexing step comprises the step of:delaying switching of the videodata in all of said predetermined number of sections except said one ofsaid predetermined number of sections for a time sufficient to enablesaid first updated communication frame to be formed.
 39. The method ofclaim 35, further comprising the steps of:receiving, at said one endterminal, a second communication frame having predetermined number ofsections for storing, respectively, audio data from a predeterminednumber of said plurality of terminals; audibly presenting the audio datain said predetermined number of sections of said second communicationframe; acquiring audio data at said one end terminal; replacing audiodata in one of said predetermined number of sections of said secondcommunication frame with the audio data acquired by said audio inputcircuit to generate a second updated communication frame; andtransmitting said second updated communication frame to said network.40. The method of claim 39, wherein said first communication frame andsaid second communication frame form respective portions of a singlecommunication frame received in said receiving steps.
 41. The method ofclaim 40, wherein said first updated communication frame and said secondupdated communication frame form respective portions of a singlecommunication frame to be transmitted by said transmitting steps. 42.The method of claim 39, wherein said audio data being replaced is audiodata previously transmitted by said end terminal.
 43. An end terminal ina teleconferencing system for communicating data along a network, saidend terminal comprising:an interface unit for receiving a communicationframe from said network, said communication frame having a predeterminednumber of sections for storing, respectively, video data from apredetermined number of end terminals in said teleconferencing system; avideo input/output unit for displaying video data and for acquiringvideo data; a controller for causing said display to operate in at leastone of a plurality of selectable modes, said plurality of selectablemodes includes:a first mode wherein said controller generates controlsignals for transmitting the video data in all of said predeterminednumber of sections of said communication frame to said videoinput/output unit for display, a second mode wherein said controllergenerates control signals for transmitting to said video input/outputunit the video data in at least one of said predetermined number ofsections of said communication frame for display along with the videodata acquired by said video input/output unit, and a third mode whereinsaid controller generates control signals for causing said display todisplay only said video data acquired by said video input/output unit; avideo replacement circuit for replacing video data in one of saidpredetermined number of sections of said communication frame with thevideo data acquired by said video input/output unit to generate anupdated communication frame; and a transmitter for transmitting saidupdated communication frame to said network.
 44. An end terminal in ateleconferencing system for communicating data along a network, said endterminal receiving from said network a communication frame having apredetermined number of sections for storing video data from respectiveones of a predetermined number of end terminals in said teleconferencingsystem, said end terminal comprising:a video input/output unit fordisplaying the video data and for acquiring video data; a controller forcausing said display to operate in at least one of a plurality ofselectable modes, said plurality of selectable modes includes:a firstmode wherein said controller generates control signals for transmittingthe video data in all of said predetermined number of sections of saidcommunication frame to said video input/output unit for display, asecond mode wherein said controller generates control signals fortransmitting to said video input/output unit the video data in at leastone of said predetermined number of sections of said communication framefor display along with the video data acquired by said videoinput/output unit, and a third mode wherein said controller generatescontrol signals for causing said display to display only said video dataacquired by said video input/output unit; a video replacement circuitfor replacing video data in one of said predetermined number of sectionsof said communication frame with the video data acquired by said videoinput/output unit to form an updated communication frame; and atransmitter for transmitting said updated communication frame to saidnetwork.
 45. A teleconferencing system for communicating videoinformation among a plurality of terminals connected to a network, saidsystem comprising:a first terminal for transmitting a communicationframe to said network, said communication frame having a predeterminednumber of sections for storing video data from respective ones of apredetermined number of said plurality of terminals; and a secondterminal including:an interface unit for receiving the communicationframe transmitted by said first terminal, a video input/output unit fordisplaying the video data and for acquiring video data, a controller forcausing said display to operate in at least one of a plurality ofselectable modes, said plurality of selectable modes includes: a firstmode wherein said controller generates control signals for transmittingthe video data in all of said predetermined number of sections of saidcommunication frame to said video input/output unit for display, asecond mode wherein said controller generates control signals fortransmitting to said video input/output unit the video data in at leastone of said predetermined number of sections of said communication framefor display along with the video data acquired by said videoinput/output unit, and a third mode wherein said controller generatescontrol signals for causing said display to display only said video dataacquired by said video input/output unit; a video replacement circuitfor replacing video data in one of said predetermined number of sectionsof the communication frame with the video data acquired by said videoinput/output circuit to generate an updated communication frame; and atransmitter for transmitting said updated communication frame to one ofsaid plurality of terminals.
 46. A method for communicating data withina teleconferencing system containing a plurality of end terminalsconnected to a network, said method comprising the steps of:receiving,at one end terminal, a communication frame from said network, saidcommunication frame having a predetermined number of sections forstoring video data from respective ones of a predetermined number ofsaid plurality of end terminals; obtaining video data at said one endterminal; displaying the video data in at least one of a plurality ofselectable modes, said plurality of selectable modes includes:a firstmode wherein the video data in all of said predetermined number ofsections of said communication frame are displayed, a second modewherein at least one of said predetermined number of sections of saidcommunication frame are displayed along with the obtained video data,and a third mode wherein only said obtained video data is displayed;replacing the video data in one of said predetermined number of sectionsof said communication frame with the obtained video data to generate anupdated communication frame; and transmitting said updated communicationframe to said network.